The invention relates to a conductive member having a first and a second material.
Hitherto, for example a FTC (Feed Through Capacitor) is used in order to eliminate a high frequency noise mixed into an electronic circuit.
When signal is inputted in FTC described above, DC and low frequency components of the input signal can hardly be attenuated, while a high frequency component of the input signals is attenuated greatly. However, this FTC shows the frequency characteristic that although the amount of attenuation of the signal is increased as the frequency of the input signal becomes high, in contrast with this, now, the amount of the attenuation is decreased when the frequency of the input signal increases. Thus, even though showing the characteristic that the amount of the attenuation is decreased, the high frequency noise can be eliminated by FTC when the frequency is not extremely high. However, in recent years, it has been required to attenuate the noise of the order of several GHz efficiently because of the increase of the clock frequency of the electronic equipment such as PC (personal computer), whereby it is hard to attenuate the noise of the order of several GHz or more efficiently by FTC described above.
The object of the invention is to provide a conductive member capable of attenuating the noise having frequency components, for example, of the order of several GHz efficiently.
To achieve the above-mentioned object, the conductive member according to the present invention has a first material and a second material, characterized in that the product of conductivity and permeability of the conductive member is larger than the product of conductivity and permeability of a conductive member having only one of both the first and second materials.
The higher the frequency of current flowing in the conductive member (e.g. the conductive wire) becomes, the more the tendency of concentrating the current on the surface side of the conductive member accelerates by a skin effect. The a skin depth xcex4 expressing the depth of the surface portion of the conductive member on which a current concentrates can be defined as the expression described below.                     δ        =                              2                          ω              ⁢                              xe2x80x83                            ⁢              σ              ⁢                              xe2x80x83                            ⁢              μ                                                          [Expression  1]            
where, xcfx89 is an angular frequency, "sgr" is conductivity and xcexc is permeability.
The product "sgr"xcexc of conductivity "sgr" and permeability xcexc of the conductive member according to the present invention is larger than the product "sgr"xcexc of conductivity xcexc and permeability xcexc of a conductive member (hereinafter, in some cases, referred to as the conductive member for comparison) having only one of both the first and second materials.
For example if silver is provided as the described-above first substance and ferrite is provided as the described-above second substance, and the conductive member has silver, as well as ferrite is provided as the conductive member. In this case, the conductive member according to the invention would have both substances of silver and ferrite. Namely, the conductive member for comparison does not have ferrite which has large permeability, on the other hand, the conductive member according to the invention has ferrite which has large permeability. Therefore, when the product "sgr"xcexc of conductivity "sgr" and magnetic permeability xcexc of this conductive member for comparison is defined as "sgr"xcexc1, on the other hand, the product "sgr"xcexc of the conductive member according to the invention is defined as "sgr"xcexc2, the skin depth xcex4 of the conductive member according to the invention can be smaller than the skin depth xcex4 of the conductive member for comparison by selecting the amount of ferrite contained in the conductive member according to the invention in such a way that "sgr"xcexc2 becomes larger than "sgr"xcexc1. Therefore, when the noise of the same frequency is fed into each of the conductive members according to the invention and the conductive member for comparison, the skin depth xcex4 at the frequency of the noise of the conductive member according to the invention becomes smaller than that of the conductive member for comparison. Accordingly, the high frequency noise can be attenuated efficiently by using the conductive member according to the invention.
Moreover, considering simply from Expression 1, in order to make the skin depth xcex4 small by increasing the product of conductivity and permeability, either the conductivity or the permeability can be increased. However, in the case of making the skin depth xcex4 small by increasing the conductivity, the high frequency noise is more accepted by the high conductivity than the small skin depth xcex4. According to the invention, it is effective for attenuating the high frequency noise to make the skin depth xcex4 small by increasing permeability without increasing the conductivity excessively. However, the low frequency signal which should not be accepted is attenuated when setting the conductivity excessively small. Therefore, the conductivity should be set on the basis of usage of the conductive member.
Preferably, according to the conductive member of the present invention, the first material is a metal and the second material is a magnetic material, and the product of conductivity and permeability of a conductive member having the metal and the magnetic material is larger than the product of conductivity and permeability of a conductive member not having the magnetic material but having the metal.
The conductive member according to the invention comprises magnetic materials, whereby the product of the conductivity and permeability of the conductive member according to the invention can be made large efficiently. That is to say, the skin depth can be made small efficiently.
Preferably, according to the conductive member of the present invention, the magnetic material is a ferromagnetic material.
The product of the conductivity and magnetic permeability can be made large further efficiently by using ferromagnetic material.